In automated parametric testing of semiconductor devices, there is a desire to collect large amounts of data from devices on wafers using a minimum set of expensive parametric test equipment shared amongst large numbers of devices. This is generally achieved by switching or multiplexing the parametric test equipment output amongst device inputs across the whole wafer, one at a time. For example, an external multiplexer may reside on top of a probe card on a wafer prober, which makes contact with a probe card through pogo pins. Conventional solutions to multiplexing the signals on top of the probe card, on the wafer prober, can use a large number of relays and switches in the construction of the multiplexer, which can be unnecessarily expensive.
FIG. 1 schematically illustrates such a conventional arrangement for testing devices on a wafer 112. Referring to FIG. 1, a parametric tester 102 has N source lines 104 connected through a pin multiplexer 106, which selects pins of a wafer prober 108 to receive the N source lines. Typically the pin selection will vary for different devices (i.e., circuit layouts) in a semiconductor wafer under control of computer 110.
For example, a conventional automatic switch matrix multiplexer may utilize N relays (the number of outputs required) per M inputs (M×N total relays). For a 4 input multiplexer, multiplexing into forty eight outputs would use 4×48 relays.
U.S. patent application Ser. No. 11/270,371, filed Nov. 8, 2005 and entitled “Semi Automatic Multiplexing System” describes an example parametric test system in which four inputs are switched into banks of four jumpers which then make manual connectivity with four of forty eight possible outputs. In this system, the input sources can only be connected to a corresponding jumper output position. For example, input 1 can only be connected to output 1 of banks 1 through 12 (in the case of 48 outputs), input 2 can only be connected to output 2 of banks 1 through 12 and so on. Each relay, though, can be actuated independently. This way, a reduction of expensive relays can be achieved but yet no flexibility is lost or sacrificed. A trivial case of this scheme is when the four input sources are hardwired to four outputs that have all forty eight outputs run across them and connected manually to the four inputs by manually placing jumpers at the grid intersections. This way, the multiplexer can be completely manual and operate without relays.